Proximity-based applications and services may have sociological and/or technological implications. At least one principle of proximity-based applications may be to discover one or more instances of the applications running in one or more devices that may be within proximity of each other. Proximity-based applications may also exchange or share application-related data or other events.
Device-to-device (D2D) communication between devices may take place after D2D-capable devices are made aware of the presence of other peer devices in their vicinity, and of the services that those devices offer and/or participate in. The discovery process may be viewed as distinct from the data communication process itself. From the radio perspective, it is possible that the device discovery may happen in a different frequency, as compared to the communication, (in this case, the judgment of the quality of the D2D link in the discovery frequency may have to be translated into a judgment of the corresponding D2D data link frequencies). One may envision discovery over a physical link between the devices, followed by communication over a local path that does not involve a direct physical D2D link. In addition, discovery may be performed by a wireless communication system, including at least one of radio access network (RAN) or core network (CN) elements, since the system may monitor the location of devices that are attached to it.
One of the main aspects of D2D communications is service discovery. The wireless transmit/receive units (WTRUs) that are involved in D2D communications need to develop a real-time awareness of their surrounding WTRUs in terms of the services that are supported by their peers. This awareness may help WTRUs to either participate or provide services to their peers. In most cases, the discovery is followed by communication, but in some cases, the discovery may be an end result in itself and need not be followed by any data communication.
Before a WTRU's D2D service may be operational, device discovery has to be performed, wherein WTRUs obtain lower layer device addresses for their neighbors that are also willing and able to participate in D2D communication. Service discovery is the process where the WTRU discovers the services that the discoverable users support and the corresponding service identities. Since service discovery is the ultimate goal of the process, it is desirable to tie device and service discovery together in the overall architecture and system design. Device and service discovery may be executed independently from one another before D2D services may be supplied, (e.g., discovery itself may be a service).